CVE-2026-73493 PUBLISHED

http4s-blaze-server: Unbounded WebSocket message aggregation

Assigner: GitHub_M
Reserved: 12.08.2026 Published: 12.08.2026 Updated: 12.08.2026

Http4s (http4s-blaze-server) is a minimal, idiomatic Scala interface for HTTP services. Prior to 0.23.18 and 1.0.0-M42, http4s-blaze-server aggregates fragments of an incoming WebSocket message with no limit on total size or fragment count. A client that completes a WebSocket handshake can send an unterminated fragmented message and drive unbounded heap growth in the server JVM, resulting in denial of service through OutOfMemoryError. Any http4s application serving WebSocket routes over BlazeServerBuilder is affected, no non-default configuration is required, and maxWebSocketBufferSize does not bound the aggregate because it bounds only individual frames. A single connection sending continuation frames that never set FIN forces the server to buffer every fragment until the heap is exhausted, terminating the JVM with OutOfMemoryError on the blaze selector thread. Small fragments amplify the cost through per-frame object overhead, so a modest volume of wire bytes is sufficient. This issue is fixed in versions 0.23.18 and 1.0.0-M42.

Metrics

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CVSS Score: 7.5

Product Status

Vendor http4s
Product blaze
Versions
  • Version < 0.23.18 is affected
  • Version >= 1.0.0-M1, < 1.0.0-M42 is affected

References

Problem Types

  • CWE-770: Allocation of Resources Without Limits or Throttling CWE